1. Technical Field
The present invention relates to a projector. 2. Related Art
In general, although image signals with various aspect ratio (a ratio between the horizontal size of an image and the vertical size thereof) are input to a projector, since the size of a liquid crystal panel for forming the image is fixed, there arises a problem that the aspect ratio of the image signal input thereto and the aspect ratio of the liquid crystal panel do not match with each other.
In the case in which the aspect ratio of the input image signal and the aspect ratio of the liquid crystal panel do not match with each other, there are known the following methods for displaying the input image signal by the projector. As a general method (related art example 1), there can be cited a method of providing blank portions (black display portions) at the top and the bottom or the left and the right of the screen. In the case in which, for example, the image signal with the aspect ratio of 4:3 is displayed on the liquid crystal panel with the aspect ratio of 16:9, the blank portions are displayed on the left and the right of the screen.
This method results in inhibition of using the entire display area of the liquid crystal panel due to the blank portions provided at the top and the bottom or the left and the right thereof, thus incurring degradation in the resolution. Specifically, in the case in which the image signal with an aspect ratio of 4:3 is displayed on the liquid crystal panel with an aspect ratio of 16:9, the horizontal resolution is reduced about 25%. By contrast, in the case in which the image signal with an aspect ratio of 16:9 is displayed on the liquid crystal panel with an aspect ratio of 4:3, the vertical resolution is reduced about 25%. Further, since the area corresponding to the blank portion is also irradiated with the illumination light constantly, it faces the problem that the life of the liquid crystal panel is apt to be shorten. Further, it also faces the problem that the illumination efficiency is reduced due to the presence of the blank portion.
Therefore, in order for solving the problem described above, there is proposed a projector, which compresses the image with an aspect ratio of 16:9 in the horizontal direction to display it on the liquid crystal panel with an aspect ratio of 4:3, then restores the image, which has been compressed once, to be an image with an aspect ratio of 16:9 via an anamorphic lens, and then projects it with a projection lens (see, e.g., JP-A-4-170178 (Document 1)). When the projector displays the image with an aspect ratio of 4:3, the image is projected by the projection lens without making the image pass through the anamorphic lens by retracting a plane mirror, which is located between the anamorphic lens and the projection lens, from the optical path. By switching the plane mirror as described above, the two types of images with aspect ratios different from each other are displayed.
Further, there is proposed a projector, which selects the most appropriate one of two aspect ratios the projector can set, based on the aspect ratio of the input signal, and rotates the anamorphic lens in accordance therewith, thereby realizing switching of the two types of aspect ratios of the display image (see, e.g., JP-A-6-253242 (Document 2)).
In the projector described in the Document 1, although such degradation in the resolution as in the related art example 1 is not caused, there is required a mechanism for switching between the anamorphic lens and the normal projection lens with the plane mirror, which makes the structure problematically complicated.
Further, in the projector described in the Document 2, although the switching mechanism is simpler compared to the projector described in the Document 1, since it can only cope with the two types of aspect ratios, and moreover, the size of the liquid crystal panel is limited by the aspect ratio to be switched to, there arises the problem that freedom of design is dramatically reduced.